Clara Clayton played by Jim.
Clara Clayton is the school teacher in the small western town of Hill Valley.
Jim is a rather gung-ho roleplayer, interested in action, cool fight scenes, and lucrative spoils over careful consideration or puzzle solving. He frequently acts before he thinks, which includes fixating on his own strange explanations for setting details that the GM hasn't explained yet.
Marty McFly played by Ben.
Marty McFly is a the son of a local farmer.
Ben is a thoughtful roleplayer who tries to think through the best course of action within his character concept and the setting. He enjoys coming up with clever ways to justify the success of his plans within the premises of the setting.
Seamus McFly played by Pete.
Seamus McFly is Marty's father.
Pete is an old friend of Jim's. Jim invited him along to join in this new game. Pete designed a character to maximise all the skills he thought would come in most useful in an American western frontier game, at the cost of having three Dependents, being Dirt Poor, and Irish.
Doc Emmett Brown played by Sally.
Doc Emmett Brown is the town blacksmith and inventor.
Sally is Ben's younger sister. Ben took her along to the game on the first evening when his parents couldn't get a babysitter for the night. The GM quickly gave her a character to play so she wouldn't get bored. She enjoys the make-believe aspect of the game, but has some trouble separating it from reality.
Maggie McFly played by Annie.
Maggie McFly is Marty's mother.
Annie is an acquaintance of Ben's, who attends his drama classes. She was interested to come along and see what this "roleplaying games" thing was all about, after Ben described it to her as a sort of improvisational acting thing. She is dedicated to playing her character as a real, complex person with motivations inspired by a well-considered backstory.
Buford "Mad Dog" Tannen.
Buford "Mad Dog" Tannen is a crazed outlaw. His main concern is recovering the $80 he lost after Doc Brown shoed his horse, Phanastacoria, and then the horse later threw a shoe and had to be shot.
Marshall Strickland is the marshall of Hill Valley. He keeps an eye on the town and tries to keep everyone out of trouble, which seems to be a very difficult thing to do with so many PCs around.
Mayor Hubert is the mayor of Hill Valley. He uses his great wisdom and popularity to build clock towers and promise to build railroad bridges (that never seen to get completed). How exactly he gets away with this is a mystery.
The Band is a trio of mysterious wandering musicians. Mayor Hubert thinks they're sharp dressed men but Clara thinks they're on their last legs. Who is right remains to be seen.